1. Field of the Invention
The present invention relates to a device for the combined blowoff of fuel and air, in particular for direct fuel injection systems of internal combustion engines.
2. The Prior Art
A device for the combined blowoff of fuel and air is described in JP 2,185,664 (A). This known device has a fuel injection nozzle having the fuel valve and the air valve directed in opposite directions. Consequently, actuation with one single electromagnet is not possible in this known device. This leads to a considerable expenditure in terms of construction, space and control in particular, for example, with multi-cylinder internal combustion engines. The two valves do in fact abut against the housing; however, the cleaning effect of the air feed line via the valve seats of the fuel valve is canceled because they open in opposite directions.
Another known injection nozzle, which is different from the present invention, is known from DE PS 273,497. In this device, both valves open inwardly. This arrangement is suitable only for internal combustion engines having very high air and fuel pressures, for example, diesel engines. With gasoline injection, such an arrangement requires an additional, extremely high, expenditure with relatively high controlling forces because the fuel valve is pressure-controlled and dependent on a pump. No provision is made here for any control with an electromagnet. Control of the air valve is otherwise accomplished mechanically by means of a cam disk.
Another device, which is also different from the invention, is known from DE 3,914,636 A1. Here, the valve body of an air valve, which is movable into the interior of a housing and which concentrically surrounds the fuel feed line, is seated on a valve surface on the blowoff aperture of the housing. The valve body of a centrally arranged fuel valve, which is facing the blowoff aperture and is outwardly movable, is seated on a sealing surface provided on the valve body of the air valve. The seats on the inner and outer sides of the valve body of the air valve are directly exposed to the heat of the combustion chamber adjoining the blowoff aperture. Thus, there is a risk that the valve seats are easily fouled by carbon accumulation or the like. Therefore, the known device is at best usable for suction tubes.
As opposed to what is stated in the published patent specification of DE 3,914,636 A1, such limited applicability ensues for another reason. Since the two valves are operable in different directions, the high pressure in the combustion chamber would cause the air valve to open when it should be closed. On the other hand, if the closing spring of the air valve were to be dimensioned sufficiently strongly, then the electromagnet, in turn, would have to have an extremely high force. Consequently, the electromagnet would have a size of such a magnitude that it would not be acceptable for reasons of space availability (i.e., in order to be capable of opening the valve without the joint action of the gas pressure).
Furthermore, the interdependent sealing between these two valves, which are actuated by a common electromagnet, and the air valve against the housing, requires a high degree of precision of a magnitude that could hardly be accomplished at high thermal stress, in addition to the high manufacturing cost of such components.
Another known device for the combined blowoff of fuel and air is described in EP 0,384,473 A1. Here, provision is made for an air valve, which is actuated by an electromagnet, at the end of a housing aperture on the blowoff side. The valve member of the air valve is seated on a valve seat of the housing. For this purpose, throttle bores are arranged in and perpendicular to the valve seat. These bores are connected with a fuel feed conduit, in which another electromagnetically actuated metering valve for the fuel feed is arranged (i.e., screwed to the housing of the device).
The known device is rather complicated because it has two metering valves with electromagnets that operate independently of each other. The valve seat is, again, unfavorably located directly on the combustion chamber, in particular, the throttle bores for the fuel, such that the valve seats can easily change or become fouled.